.\" $OpenBSD: X509_get0_signature.3,v 1.9 2024/08/28 07:18:55 tb Exp $
.\" selective merge up to:
.\" OpenSSL man3/X509_get0_signature 2f7a2520 Apr 25 17:28:08 2017 +0100
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.Dd $Mdocdate: August 28 2024 $
.Dt X509_GET0_SIGNATURE 3
.Os
.Sh NAME
.Nm X509_get0_signature ,
.Nm X509_REQ_get0_signature ,
.Nm X509_CRL_get0_signature ,
.Nm X509_get0_tbs_sigalg ,
.Nm X509_CRL_get0_tbs_sigalg ,
.Nm X509_get_signature_type ,
.Nm X509_get_signature_nid ,
.Nm X509_REQ_get_signature_nid ,
.Nm X509_CRL_get_signature_nid ,
.Nm X509_get_signature_info
.Nd signature information
.Sh SYNOPSIS
.In openssl/x509.h
.Ft void
.Fo X509_get0_signature
.Fa "const ASN1_BIT_STRING **psig"
.Fa "const X509_ALGOR **palg"
.Fa "const X509 *x"
.Fc
.Ft void
.Fo X509_REQ_get0_signature
.Fa "const X509_REQ *req"
.Fa "const ASN1_BIT_STRING **psig"
.Fa "const X509_ALGOR **palg"
.Fc
.Ft void
.Fo X509_CRL_get0_signature
.Fa "const X509_CRL *crl"
.Fa "const ASN1_BIT_STRING **psig"
.Fa "const X509_ALGOR **palg"
.Fc
.Ft const X509_ALGOR *
.Fo X509_get0_tbs_sigalg
.Fa "const X509 *x"
.Fc
.Ft const X509_ALGOR *
.Fo X509_CRL_get0_tbs_sigalg
.Fa "const X509_CRL *crl"
.Fc
.Ft int
.Fo X509_get_signature_type
.Fa "const X509 *x"
.Fc
.Ft int
.Fo X509_get_signature_nid
.Fa "const X509 *x"
.Fc
.Ft int
.Fo X509_REQ_get_signature_nid
.Fa "const X509_REQ *req"
.Fc
.Ft int
.Fo X509_CRL_get_signature_nid
.Fa "const X509_CRL *crl"
.Fc
.Ft int
.Fo X509_get_signature_info
.Fa "X509 *x"
.Fa "int *md_nid"
.Fa "int *pkey_nid"
.Fa "int *security_bits"
.Fa "uint32_t *flags"
.Fc
.Sh DESCRIPTION
.Fn X509_get0_signature ,
.Fn X509_REQ_get0_signature ,
and
.Fn X509_CRL_get0_signature
set
.Pf * Fa psig
to the signature and
.Pf * Fa palg
to the signature algorithm of
.Fa x ,
.Fa req ,
or
.Fa crl ,
respectively.
.Fn X509_get0_tbs_sigalg
and
.Fn X509_CRL_get0_tbs_sigalg
return the signature algorithm in the signed portion of
.Fa x
or
.Fa crl ,
respectively.
The values returned are internal pointers
that must not be freed by the caller.
.Pp
.Fn X509_get_signature_type
returns the base NID corresponding to the signature algorithm of
.Fa x
just like
.Xr EVP_PKEY_base_id 3
does.
.Pp
.Fn X509_get_signature_nid ,
.Fn X509_REQ_get_signature_nid ,
and
.Fn X509_CRL_get_signature_nid
return the NID corresponding to the signature algorithm of
.Fa x ,
.Fa req ,
or
.Fa crl ,
respectively, just like
.Xr EVP_PKEY_id 3
does.
.Pp
.Fn X509_get_signature_info
retrieves information about the signature of certificate
.Fa x .
The NID of the digest algorithm is written to
.Pf * Fa md_nid ,
the public key algorithm to
.Pf * Fa pkey_nid ,
the effective security bits to
.Pf * Fa security_bits ,
and flag details to
.Pf * Fa flags .
Any of the output parameters can be set to
.Dv NULL
if the information is not required.
If
.Fa flags
is not a
.Dv NULL
pointer,
.Pf * Fa flags
is set to the bitwise OR of:
.Bl -tag -width 1n -offset 3n
.It Dv X509_SIG_INFO_VALID
No error occurred.
This flag is set if
.Fn X509_get_signature_info
returns 1.
.It Dv X509_SIG_INFO_TLS
The signature algorithm is appropriate for use in TLS.
For a supported EdDSA algorithm (in LibreSSL this is Ed25519)
this flag is always set.
For an RSASSA-PSS PSS algorithm this flag is set if
the parameters are DER encoded,
the digest algorithm is one of SHA256, SHA384, or SHA512,
the same digest algorithm is used in the mask generation function,
and the salt length is equal to the digest algorithm's output length.
For all other signature algorithms this flag is set if the digest
algorithm is one of SHA1, SHA256, SHA384, or SHA512.
.El
.Pp
.Fn X509_get_signature_info
returns 1 on success and 0 on failure.
Failure conditions include unsupported signature algorithms,
certificate parsing errors and memory allocation failure.
.Pp
These functions provide lower level access to the signature
for cases where an application wishes to analyse or generate a
signature in a form where
.Xr X509_sign 3
is not appropriate, for example in a non-standard or unsupported format.
.Sh SEE ALSO
.Xr EVP_PKEY_base_id 3 ,
.Xr OBJ_obj2nid 3 ,
.Xr X509_ALGOR_new 3 ,
.Xr X509_CRL_get0_by_serial 3 ,
.Xr X509_CRL_new 3 ,
.Xr X509_get_pubkey 3 ,
.Xr X509_get_subject_name 3 ,
.Xr X509_get_version 3 ,
.Xr X509_new 3 ,
.Xr X509_REQ_new 3 ,
.Xr X509_sign 3 ,
.Xr X509_signature_dump 3 ,
.Xr X509_verify_cert 3
.Sh HISTORY
.Fn X509_get_signature_type
first appeared in SSLeay 0.8.0 and has been available since
.Ox 2.4 .
.Pp
.Fn X509_get0_signature
and
.Fn X509_get_signature_nid
first appeared in OpenSSL 1.0.2.
.Fn X509_REQ_get0_signature ,
.Fn X509_CRL_get0_signature ,
.Fn X509_get0_tbs_sigalg ,
.Fn X509_REQ_get_signature_nid ,
and
.Fn X509_CRL_get_signature_nid
first appeared in OpenSSL 1.1.0.
All these functions have been available since
.Ox 6.3 .
.Pp
.Fn X509_CRL_get0_tbs_sigalg
first appeared in LibreSSL 3.7.1 and has been available since
.Ox 7.3 .
.Pp
.Fn X509_get_signature_info
first appeared in OpenSSL 1.1.1 and has been available since
.Ox 7.6 .
.Sh CAVEATS
The security bits returned by
.Fn X509_get_signature_info
refer to the information available from the certificate signature
(such as the signing digest).
In some cases the actual security of the signature is smaller
because the signing key is less secure.
For example in a certificate signed using SHA512
and a 1024-bit RSA key.
